This invention relates in general to xerography and more specifically to a novel photosensitive device.
In recent years, interest has been shown in flexible electrophotographic plates for use in high speed office copying machines. Some of these plates are multilayered devices comprising, a conductive substrate layer, an adhesive-blocking interface layer, a charge generation layer and a charge transport layer. The charge transport layer comprises an organic charge transport molecule dissolved in a polymeric matrix material. This layer is substantially nonabsorbing in the spectral region of intended use, i.e. visible light, but is "active" in that it allows (1) injection of photogenerated holes from the charge generation layer and (2) efficient transport of these charges to the surface of the transport layer to discharge a surface charge thereon.
One class of hole transport molecules, N,N'-diphenyl-N,N'-bis(alkylphenyl)-[1,1'-biphenyl]-4,4'-diamines, has been extensively studied as solutions or dispersions in polycarbonate polymers. The conductivity of this class of compounds in polycrbonate polymers has been found to increase under certain circumstances. When photoreceptor devices employing this class of compounds have a residual amount of a halogen-containing alkane solvent in the transport layer and they are subjected to ultraviolet radiation, a condition known as "cycle down" progressively develops as the device is cycled in the xerographic process. "Cycle down" refers to the progressive increase in conductivity of the transport layer and in a relatively short period of time the charge acceptance of the device deteriorates. Also, special precautions have to be taken with regard to the handling of the devices employing these compounds. They cannot be stored or left exposed to ambient room light for any length of time because fluorescent lamps employed in most buildings contain a UV component. This UV radiation causes devices left exposed to the room light to undergo gradual deterioration resulting in an increase in the conductivity of the transport layer.